V1 conveys the Mode A Code in a Test Message, i.e. FTC=23, subcode=7 under adsbVersion=1.
Bits 9-21 (inclusive) contain the 13 bit Mode A Code in the same format as the 13 bit code that was later (i.e. in V2) broadcast in the extension of the Emergency And Priority Status message.
V1 conveys the Mode A Code in a Test Message, i.e.
FTC=23,subcode=7underadsbVersion=1.Bits 9-21 (inclusive) contain the 13 bit Mode A Code in the same format as the 13 bit code that was later (i.e. in V2) broadcast in the extension of the Emergency And Priority Status message.